Sealants useful in aerospace and other applications must satisfy demanding mechanical, chemical, and environmental requirements. The sealants can be applied to a variety of surfaces including metal surfaces, primer coatings, intermediate coatings, finished coatings, and aged coatings. In sealants such as those described in U.S. Pat. No. 6,172,179 thiol-terminated polythioethers and polyepoxy curing agents are reacted to provide cured aerospace sealants.
In practice, sealant compositions can be provided as two-part compositions in which the thiol-terminated polythioethers and the polyepoxy are provided as separate components, with the base catalyst in the polythioether component. Alternatively, the base catalyst may be provided as a third component, and the component containing the thiol-terminated polythioether, the component containing the polyepoxy, and the component containing the base catalyst are mixed shortly before use. However, once the components are mixed, the reaction proceeds, and depending at least in part on the temperature and on the type of base catalyst, the pot life is limited to less than 12 hours.
Ways to prolong the pot life of thiol-terminated polythioether compositions employing epoxy curing chemistries are desired.